Add option to pass in location of runtime log

Background: On Jenkins, each new branch gets a new workspace folder. This means that the tests have to start from scratch with runtime grouping.

This change allows the location of the runtime log (to be read*) to be set using the cli option:

    --runtime-log [PATH]

Hence runtimes can be shared between builds, and for the first build of a new branch.

\* The output location for the log can be manipulated by setting the output location for the formatter